Recently, multi-channel audio signals such as 5.1-channel audio signals are recorded in some audio sources such as DVDs. Multi-channel sound reproducing systems for reproducing such audio sources have been coming into wide use even in general homes. In such a multi-channel sound reproducing system, a multi-channel sound reproducing effect expected by an audio equipment maker can be obtained when respective speakers are disposed in a listening room according to a layout method recommended by the maker. It is therefore likely that sound image localization will be out of place if the layout of the speakers is greatly different from the recommended layout.
Therefore, there has been proposed a sound image localization adjusting apparatus in which positions of speakers are detected, and a correction process is performed on audio signals output from the speakers based on the detected positions so as to correct the sound image localization (for example, see Patent Document 1).
Prior to filing of this description, the present inventor had found no prior-art document pertaining to the present invention except the prior-art document specified in prior-art document information described in this description.    Patent Document 1: JP-A-11-113099
However, the sound image localization adjusting apparatus in Patent Document 1 detects positions of speakers in a one-dimensional detection method in which the distance between an amplifier and each speaker is measured based on the length of a speaker cable. The sound image localization adjusting apparatus does not detect the positions of the speakers two-dimensionally or three-dimensionally. According to the sound image localization adjusting apparatus in Patent Document 1, it is therefore impossible to obtain an angle of each speaker with respect to an optimal listening position. Even if this angle is greatly different from that in a recommended position, the inappropriate layout of the speakers cannot be detected. Thus, there is a problem that only an in adequate sound image localization correction process can be performed.